What "mom" factor, there was none of that? The whole hair style in IM 2 made her look like a girl playing dress up, not a badass spy. The we get to Avengers and I thought "yeah, that works much better." Personally, I prefer BW with shorter hair. She's always been practical and pragmatic and shorter hair would work better in her line of work.

I get that shorter would work better for women in battle
Although, pulled back tight, like female soldiers, would probably be even more practical
and IDK, it's that short bob, a lotta my friends mom's had that haircut when I was little, guess that's why it screams "MOM-HAIR" to me